(^ Index)

Talks in this session:

  1. Rafalski: Sirt1 in adult neural stem cells
  2. Charville: Non-random chromosome segregation in skeletal muscle precursor cells
  3. Xie: Connecting molecular markers and morphological changes to the lifespan of individual yeast cells

Victoria Rafalski (Stanford; Brunet lab) — Sirt1 in adult neural stem cells

Cognitive decline occurs with age: speed of processing, working memory, and long-term memory all decline. Presumably cell loss is partially to blame – not only loss of neurons, but also other types of cells (e.g., oligodendrocytes). Neural stem cells (NSC) can regenerate lost cells to some extent, but their ability to do so diminishes with age.

The Brunet lab is looking at the idea that pathways that control lifespan in “lower” organisms (worms; yeast) may be involved in regenerative capacity in “higher” organisms (us; mice). Rafalski’s work is focusing on the now-famous SIRT1. SIRT1 is downregulated over the course of differentiation, so there’s a smoking gun – but is there a causative relationship between SIRT1 downregulation and loss of regenerative capacity in NSCs?

Rafalski has constructed a mouse with a brain-specific deletion of SIRT1. Her metabolic labeling experiments show that loss of SIRT1 results in increased NSC proliferation in part of the brain called dentate gyrus – leading to the hypothesis that SIRT1 prevents the premature proliferative exhaustion of the NSC pool – in other words, SIRT1 prevents early cell division in order to preserve replicative capacity for late life. She also asked whether SIRT1 plays a role in differentiation. Loss of SIRT1 increases the number of oligodendrocytes, probably because in the absence of SIRT1 there are more oligodendrocyte precursors in the brain.

Overall, the findings point toward a role for SIRT1 in maintaining regenerative capacity in the brain. Hopefully, future experiments will explore the functional role of this pathway in maintenance of cognitive function throughout the aging – e.g., do mice that lack neuronal SIRT1 undergo more rapid cognitive decline than wildtype? (From previously published work on whole-organism knockdowns, it appears that the mice do indeed have memory deficits.)

  • Moving from neural stem cells to muscle stem cells…

Greg Charville (Stanford; Rando lab) — Non-random chromosome segregation in skeletal muscle precursor cells

Satellite cells are committed adult muscle stem cells. Under normal conditions they are senescent, but upon injury they rapidly proliferate into myoblasts, which in turn beget muscle.

Proliferating muscle precursor cells divide asymmetrically, to regenerate the satellite cell and produce a new myoblast. During this division, chromosomes are also segregated asymmetrically. Charville used a clever and subtle metabolic labeling approach to demonstrate that newly synthesized chromosomes are preferentially segregated to one of the two sister nuclei generated in this asymmetric division.

Why does this happen? Charville explored the hypothesis that the nonrandom segregation was a function of persistent DNA damage. Activated muscle precursor cells exhibit replication-associated DNA damage, and the markers of DNA damage localize asymmetrically in the sister nuclei. The Numb protein, a pro-differentiation factor that also is an inhibitor of the Notch pathway, cosegregates with markers of DNA damage. Numb stabilizes p53, so this protein could be orchestrating the more robust DNA damage response required in the more damaged sister nucleus. It is not yet known how these asymmetries influence the cells’ ultimate fate (in the sense of differentiation).

Overall, Charville hypothesizes that this phenomenon serves to maintain the genomic integrity of the stem cell population.

  • And now on to a (somewhat) simpler system…

Zhengwei Xie (UCSF; Li lab) — Connecting molecular markers and morphological changes to the lifespan of individual yeast cells

Yeast have proven an important model system in the study of aging; budding yeast undergo asymmetric divisions in which the mother (old) and daughter (new) can be distinguished, allowing a study of replicative aging in a genetically tractable system.

Xie has developed a microfluidic system for studying yeast aging. Mother cells are immobilized with streptavidin, while daughter cells are washed away; this allows the direct observation of an aging population of mother cells – how many daughters does each mother produce? What is the division timing? The system also allows Xie to measure lifespan in an automated manner, and simultaneously follow fluorescently labeled proteins, cell morphology, and staining for a variety of other phenotypes (ROS, mitochondria).

Using this system, Xie has shown that lifespan is negatively correlated with the activity of the HSP104 promoter, in particular with the levels of a specific transcriptional factor that acts on that promoter. He has also observed progressive mitochondrial abnormalities arising in old mother cells: Old mothers contain “blobs” that contain mitochondrial protein markers but not mitochondrial DNA.

The microfluidics system is very powerful, allowing temporal sequencing of molecular events in single cells. Exploiting this power, Xie demonstrated that the HSP104 promoter is induced after the appearance of the mitochondrial blobs, suggesting that the high HSP104 activity may be a marker of a stressed or moribund cell. Indeed, cells with damaged mitochondria appear to have elevated levels of reactive oxygen species (ROS).

(Next session –>)

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Today I’ll be live-blogging the Bay Area Aging Meeting being held at Stanford.

Each session will have its own article; this entry will serve as a central hub for all related entries – the links below will go live as soon as the sessions start.

The organizers have encouraged me to blog the talks, as I did last year. More importantly, we’re hoping that the conference attendees (and others following along elsewhere in the world) will chime in via the internet.

There are two main ways to play along: in the comments below each session entry, and via Twitter.

If you’re tweeting during the talks, mark your tweets with the hashtag #baam10. (Even if you’re not tweeting, you can use the hashtag to follow the tweetstream here.) If you have no idea what I’m talking about, don’t worry about it. Follow along as the blog entries emerge, or just sit back and enjoy the conference.

(For the liveblog of the meeting as it unfolds, see here.)

Earlier this year, the biogerontologists of the San Francisco Bay Area held the first of a series of biannual research meetings, the Bay Area Aging Club. More or less right on schedule, the next meeting is in a couple of weeks on Saturday, December 4th.

It’s now the slightly more official-sounding Bay Area Aging Meeting, but the format is the same: A full day of talks from labs from all around the Bay Area, with lunch, and an opportunity to network with the large and growing local community of researchers in biogerontology and allied subjects. Last time the meeting was at UCSF; this time it’s at Stanford.

Here’s the initial event announcement from Stuart Kim. Note the registration link, which contains more detailed information about time and location. Registration is free.

Eric Verdin (Gladstone), Danica Chen (Berkeley) and I are organizing the next Bay Area Aging Meeting. This is a one day meeting to hear talks from students and post-docs from the Bay Area on aging. The meeting is on Saturday Dec. 4, 2010 at Stanford University, from 900 am to 5 pm. The last meeting in April at Gladstone was very successful with about 150 attendees.

There will be talks from students/post-docs in Bay Area Aging labs, as well as a poster session. The labs and topics are:

lab/topic
Brian Kennedy (Buck) Yeast aging
Simon Melov (Buck) worm aging
Martin Brand (Buck) mitochondrial biochemistry
Melanie Ott (Gladstone)SirT1 in T cells
Bob Farese (Gladstone) mouse metabolism
Cynthia Kenyon (UCSF) worm aging
Hao Li (UCSF) systems biology of yeast aging
Kunxin Luo (Berkeley) P53 and aging
Randy Schekman (Berkeley) intracellular traficking of APP
Anne Brunet (Stanford) mouse, worm or fish aging
Tom Rando (Stanford) stem cells and aging
Mark Davis (Stanford) human immune aging

Please reserve the day for the meeting. We will send out more information including the schedule soon. To receive more information about the meeting, register for the meeting, and sign up to give a poster, please go to:

https://www.onlineregistrationcenter.com/register.asp?m=288&c=2

Sincerely,
Eric, Danica and Stuart

The April meeting was a lot of fun. I live-blogged the event, which definitely kept my fingers flying. This year I’ll be doing that again, with some degree of official blessing/support. We’ll make some kind of an announcement at the beginning of the talks directing people to Ouroboros and encouraging them to participate in comments on the posts for each session or talk. I’ll also be spreading the word Twitter and/or FriendFeed, using hashtag #baam10, and hoping that others join in that as well.

Please come! The organizers want to reach “hard core aging people,” so if your research falls under that umbrella, register now. For a sense of how the meeting went last time, here are my posts:

P.S.: There’s no official website for BAAM yet. I’m thinking of whipping something up for them – basically for announcements and abstracts – but if anyone with experience would like to pitch in, drop me a line in the comments.

After a great deal of early promise, resveratrol has been on the ropes for a while, most prominently as a result of studies questioning whether it can directly activate sirtuins — this against a backdrop of growing skepticism that sirtuin activation can extend mammalian lifespan in any case.

Now, another (possible) black eye: GlaxoSmithKline (the company that purchased Sirtris, a pharmaceutical company co-founded by sirtuin/resveratrol pioneer David Sinclair) has suspended a trial of a resveratrol formulation, SRT501 in multiple myeloma patients, because several of the study’s subjects developed kidney failure.

GSK emphasizes that the trial has not been cancelled, but they are observing a moratorium on recruiting new patients until they determine whether the resveratrol was responsible for the subjects’ kidney problems. Nephropathy is a frequent complication in myeloma; one hypothesis being entertained is that the very high doses of resveratrol used in the trial caused vomiting, which in turn resulted in dehydration and tipped the balance in kidneys already close to failure due to the underlying cancer.

More elsewhere:

(previous session)

At the end of the meeting, Martin Brand and Stuart Kim led a group discussion about the free radical theory of aging. Martin began the discussion by pointing out that “after 50 years, you would expect a theory to accumulate enough evidence to convince us that it’s true or false – but the fact that we’re still discussing it today means that hasn’t happened.” I’m paraphrasing slightly, but that’s the general idea.

Martin Brand (who doesn’t, by the way, adhere to this theory) started by summarizing the evidence in favor of FRTA:

  • “50 million Frenchmen can’t be wrong” (i.e., there are lots of correlative experiments)
  • SOD2 knockout is bad
  • catalase overexpression is good

Stuart rejoined with some contradicting evidence:

  • Superoxide dismutase protects against oxidative stress but has little effect on lifespan in mice
  • Deletion of mitochondrial SOD extends lifespan in C. elegans
  • High oxidative damage levels in the longest-living rodent, the naked mole-rat.

To the last of which, others answered:

  • The naked mole rat isn’t suffering from a global increase in oxidative damage – rather, there are a small number of proteins with increased damage, which may represent antioxidant proteins protecting the rest of the cell
  • There’s no evidence that naked mole rats increase damage with age, which is a more relevant metric

The first two pieces of Stuart’s contradicting evidence were more difficult to challenge. Some ideas:

  • Overexpressing an antioxidant enzyme in the wrong subcellular compartment wouldn’t be predicted to have any effect on lifespan

Martin also asked questions about whether FRTA is even falsifiable, and lamented the absence of an alternative clear, single-sentence “singular” theory of aging.

No final resolution but on the balance it seems like the theory is on the ropes, as we’ve discussed here before.

(previous session)

Craig Skinner (Lin Lab, UC Davis): Identification of potential calorie restriction mimics in yeast using a nitric oxide-based screen. Yeast are an important model system in biogerontology, useful not only for genetic studies of longevity control but also for discovery of bioactive compounds. Calorie restriction (CR) in yeast causes increased levels of nitric oxide (NO) — somewhat surprising in that yeast cells lack a homolog of nitric oxide synthase — and elevated NO is sufficient to extend yeast lifespan. These observations led Skinner to screen a yeast deletion library for elevated NO levels, yielding several genes that extend lifespan.

Mark Lucanic (Lithgow Lab, Buck): Endocannabinoid signaling mediates the effect of diet on lifespan in C. elegans. Mutants in the dauer pathway in C. elegans often influence longevity; the daf-2 mutation, which causes constitutive dauer formation at elevated temperatures, extends lifespan by several fold. Lucanic discovered that endocannabinoids are involved in the regulation of the dauer pathway — and therefore, of longevity — either independently of or far downstream of daf-2 and daf-16. Endocannabinoids are upregulated under well-fed conditions, and shorten lifespan.

Delia David (Kenyon Lab, UCSF): Widespread protein aggregation is an inherent part of aging in C. elegans. Protein aggregates are a hallmark of many age-related neurodegenerative diseases, leading to the hypotheses that the cellular mileu changes with age in a manner that causes native, aggregation-prone proteins to form aggregates. David used mass spectrometry to identify a subset of normal worm proteins aggregate as a function of age. As with the proteins associated with neurodegeneration, specific proteins aggregate in specific cell types. Mutations that extend lifespan (such as daf-2) decrease aggregation, and tend to downregulate the expression of genes encoding aggregation-prone proteins. Curiously, regulators of protein homeostasis tend to aggregate themselves, leading to a destructive positive feedback loop in which the very factors that protect the cell from proteotoxicity disappear into aggregates, leading to further aggregation.

Cherry Tang (Zhong Lab, Berkeley): The Clearance of Ubiquitinated Protein Aggregates Via Autophagy. Autophagic protein degradation has been implicated in control of lifespan: autophagy slows cell and tissue aging. Tang has identified a protein that participates in degradation of ubiquitinated proteins and co-localizes with autophagosomes; when the protein is knocked down, protein aggregates become more toxic.

(next session)

(previous session)

Matt Hirschey (Verdin Lab, UCSF-Gladstone): Lack of SIRT3 results in the metabolic syndrome. SIRT3 is a mitochondrial sirtuin (NAD+-dependent deacetylase) that is upregulated in liver upon fasting; knockout mice (SIRT3KO) are grossly normal but have trouble with lipid metabolism (specifically, beta-oxidation). Hershey identified several mitochondrial proteins involved in lipid oxidation that are deacetylated in response to fasting, in wildtype but not SIRT3KO. The knockouts are prone to developing obesity and metabolic syndrome with age.

Kate Brown (Chen lab, UC-Berkeley): Calorie restriction reduces oxidative stress by inducing SIRT3. Beginning with an invocation of the free radical theory of aging, and the observation that calorie restriction (CR) reduces oxidative stress, Brown asked whether the mitochondrial sirtuin SIRT3 could be involved in resistance to reactive oxygen species. She showed that CR induces SIRT3 expression, and that the SIRT3 protein deacetylates the mitochondrial antioxidant enzyme SOD2. Furthermore, consistent with Subhash Katewa’s talk in the first session, she demonstrated that CR reduces oxidative stress by switching from glucose to fatty acid oxidation, and that this switch requires SIRT3 activity.

(We’ve discussed SIRT3 before, most recently regarding its role as a tumor suppressor and also with respect to its relationship with exercise).

Ruth Tennen (Chua lab, Stanford): Insight into SIRT6 function at telomeres and beyond. Another member of the sirtuin family, SIRT6, is not localized to mitochondria but rather to telomeres, where it maintains telomeric chromatin in a healthy state and regulates the activity of the senescence-associated transcription factor NF-κB – for more background, see this previous post.) Tennen has shown that SIRT6 is involved in regulating the telomere position effect (TPE) – the silencing of gene expression caused by proximity to a telomere. The TPE has been implicated in age-related changes in gene expression: as telomeres shorten over time, telomere-proximal genes are aberrantly expressed — meanwhile, silencing factors are liberated to wander throughout the genome, repressing genes that should be turned on; similar logic has been applied to the relationship between DNA damage and transcriptional dysregulation.

Jue Lin (Blackburn Lab, UCSF): Telomere length maintenance and aging-related diseases. This talk described work that builds on significant progress, from this lab and others, demonstrating relationships between telomere length and stress, psychological outlook, and lifespan. Lin reviewed evidence that perceived stress is correlated with telomere length in white blood cells (consistent with previous results showing a relationship with intrusive thoughts). New-to-me data included a demonstration that people who increased omega-3 levels or made favorable lifestyle changes exhibited a slower rate of telomere shortening.

(next session)